1. Field of the Invention
The present invention relates to a reception apparatus that adopts a diversity system involving a plurality of antennas, and more particularly to a reception apparatus for reproducing pictures.
2. Description of Related Art
A conventional reception apparatus is provided with a tuner circuit 10, which includes: a BPF (band-pass filter) 2 that selects from the radio-frequency signals received via an antenna 1 those within a desired frequency band; an RF amplifier 3 that amplifies the radio-frequency signals that have passed through the BPF 2; a BPF (band-pass filter) 4 that selects from the radio-frequency signals amplified by the RF amplifier 3 those within the desired frequency band; a mixer 5 that selects from the radio-frequency signals having passed through the BPF 4 the broadcast signal having a desired channel frequency; a VCO (voltage-controlled oscillator) 6 that feeds a local oscillation signal to the mixer 5; and a PLL (phase-locked loop) 7 that feeds a tuning voltage to the BPFs 2 and 4 and to the VCO 6.
The broadcast signal of the desired channel thus selected by the tuner circuit 10 configured as described above is then, as an intermediate-frequency signal (IF signal), outputted to a demodulator circuit 11 so as to be demodulated. The demodulated signal is then decoded by a decoder circuit 12 into video and audio signals, according to which pictures and sounds are reproduced on a display and from loudspeakers. When the reception apparatus shown in FIG. 8 is applied to an appliance, such as a car-mounted or portable television set or a portable telephone, that conducts communication while moving around, since the apparatus has only one antenna, reception condition greatly varies according to the position and orientation of the antenna 1. When reception condition is poor, it is not possible to reproduce pictures and sounds properly.
Such variation of the reception condition of an antenna can be dealt with by adopting a conventionally known diversity system (see Japanese Patent Application Laid-Open No. H10-84297). The configuration of a reception apparatus that adopts a diversity system is shown in FIG. 9. The reception apparatus shown in FIG. 9 is provided with: antennas 1a and 1b; tuner circuits 10a and 10b that are each configured like the tuner circuit 10 in FIG. 8; demodulator circuits 11a and 11b that demodulate the IF signals fed from the tuner circuits 10a and 10b, respectively; a comparison circuit 13 that compares the signals demodulated by the demodulator circuits 11a and 11b to determine which of the antennas 1a and 1b is yielding better reception condition; and a decoder circuit 12.
In this configuration, the IF signals that are produced from the broadcast signal of the same channel but that are selected separately by the tuner circuits 10a and 10b are demodulated by the demodulator circuits 11a and 11b, and are then fed to the comparison circuit 13. The comparison circuit 13 compares the S/N ratios and bit error rates of the signals fed from the demodulator circuits 11a and 11b, and thereby checks which of the antennas 1a and 1b is yielding better reception condition. Thus, of the demodulated signals, one that is found to be yielding better reception condition by the comparison circuit 13 is selected and is then fed to the decoder circuit 12. In this way, it is possible to reproduce pictures and sounds always from a broadcast signal that is yielding the best reception condition at the moment.
As described above, in the reception apparatus configured as shown in FIG. 9, the tuner circuits 10a and 10b each select the broadcast signal of the same channel and produce separate IF signals; moreover, the demodulator circuits 11a and 11b demodulate identical IF signals. With this configuration, it is indeed possible to select and output the broadcast signal received by an antenna that is yielding the best reception condition at the moment; however, it is not possible to receive and reproduce the broadcast signals of different channels simultaneously. Conventionally, to receive and reproduce the broadcast signals of different channels simultaneously, there is no choice but to provide so many reception apparatuses configured as shown in FIG. 9 as there are channels of which the broadcast signals are to be reproduced simultaneously. Thus, reproducing the broadcast signals of n channels requires n×2 tuners.